Cell migration is a major driving force in embryonic development, wound healing, and tumor metastasis. Therefore understanding the molecular mechanisms that control whether, when, and where cells move is significant for human health and disease. My laboratory has developed a relatively simple and genetically tractable model for the study of the developmental regulation of cell motility, the movement of a small group of cells in the Drosophila ovary known as the border cells. We have identified steroid hormone, cytokine and growth factor signaling pathways that are required for the spatial and temporal regulation of border cell migration. In the previous funding period we showed that integration of steroid hormone and cytokine signaling governs the developmental timing of border cell migration. We found that continuous signaling through the JAK/STAT pathway is required not only to specify the migratory population initially, but also to sustain motility throughout their migration. We made a significant advance by succeeding for the first time in time-lapse, live- imaging of border cell migration. Live-imaging has revealed several phenomena that were not evident in fixed samples, including that the process of detachment from the epithelium is long, slow and likely complex at the molecular level. For the cells to detach, we find that a sharp cell fate distinction must be made between cells that will migrate and those that will not. In a genetic screen for mutants that affect border cell development and migration, we identified the gene apontic as playing a critical role in this distinction. We further discovered that Apontic functions as a feedback inhibitor of JAK/STAT signaling that limits the migratory population, a process for which we developed a mathematical model and computer simulations that faithfully reproduce wild-type and mutant conditions. In our first specific aim we propose to test specific predictions of our model for Apt function and its interactions with SLBO and STAT. In aims 2 and 3, we propose to investigate the molecular mechanisms underlying the processes of detachment and directional guidance, respectively. Together these studies should significantly advance our understanding of the mechanisms that control collective cell movements, which we propose differ significantly from those controlling individual cells. PUBLIC HEALTH RELEVANCE: The ability to move is a property of cells from virtually all animals, from simple ones such as flies and worms, all the way to humans. The proposed research focuses on the movement of a small group of cells in the fruit fly, to learn more about how specific molecules orchestrate when, where and how they move. Since cell motility contributes to wound healing and tumor metastasis, these studies could lead to the discovery of new drug targets that could promote healing or inhibit the spread of cancer cells.